How can I build a .5V/.3amp to 3V/.03amp power supply, For charging two ni-cad aaa's off of a radioshack solar panel

110100101108 years ago
maybe joule thief with mosfet (0.5 V is not enough for transistor) if the panel is array of small panels maybe one is bad. measure the voltage on each and if there is bad one skip it try to add panels to get atleast 1 V
chief tyrol (author)  110100101108 years ago
It's actually only one panel, I didn't notice that the volts were too low until after I bought it, and I was hoping to avoid buying 1, or 2 more $6 panels. I found an old broken solar light that still had a functioning panel, so I just going to go ahead and use that, because it puts out a full three volts. as another question, will a joule thief charge ni-cad batteries? because I don't know how often it will be in full sun, and I don't want the voltage dropping too low and not charging. Thanks!
overall nicds dont like this kind of use. they lose capacity. the issue is called memory effect but maybe the application is easy enough on the batteries that they wont mind much. what do you use them for ? you can find wireless phone nicd batteries (in not very good but ok tolight leds condition) in the battery recycle box or place where batteries are thrown away low capacity nimh batteries are better i think cell phone li-ion batteries can be found in recycle box too. they dont like uncontrolled charge (sometimes they overheat and explode) but the power from tiny solar cell is not enough to make that happen. they dont have memory effect and are ok for most applications
Hmmm... sounds like you need to find out more about 'memory effect', for example:


Basically, 'memory effect' is largely a myth.

Anyway, I don't think a 'Joule thief' will be sufficient to charge your batteries. The current will be too low for this. However, it is sufficient just for a 'trickle charge'. If you worried for voltage dropping too low, simply use schottky diode, it's the best solution.

Unfortunately, the only solution for your battery charging, is to upgrade your solar cell, that is capable to give at least 100mA under full sun.

For voltage booster @0.5V input, that is definitely a hard ask :). National Semiconductor has nice regulated voltage booster starting from 0.9V though, just google LM2623, and use application note AN1221, April 2002 edition. Unfortunately, it's an adventure to surface mount realm.